Circularly-polarized antennas are well known in the antenna community as having forms ranging from cross-dipoles, helixes, and crossed slotted cylinders, for example. A particularly elegant circularly-polarized antenna is the stub-loop antenna which consists of a metal wire formed in the shape of a horizontal ring, with vertically opposing dipole arms at the end of the ring. The characteristics of the stub-loop antenna are primarily a function of the feed strap position on the horizontal ring and dipole stub length, wherein the VSWR and the horizontal versus vertical polarization ratio of the antenna are both affected by manipulation of either of these two parameters. Consequently, tuning of a conventional stub-loop antenna unavoidably results in a tradeoff between the desired VSWR response and the desired Horizontal Vertical (H/V) polarization ratio.
Due to this difficulty, conventional stub-loop antennas are not well suited to accommodating the FCC's equal H/V ratio rule. Furthermore, conventional stub-loop antennas have the added problem of having an inherently high downward radiation pattern. The conventional approach to remedy this latter effect have involved the implementation of reduced spaced arrays, such as, half wave spacing between adjacent stub-loop antennas. Obviously, this results in requiring nearly twice the number of stub-loop antennas as in a full wave spaced array to obtain the same respective gain, and additional feed lines and connections for the added stub-loop antennas when fed in a branch-feed configuration. All of these factors have plagued conventional stub-loop antenna systems and have accordingly rendered them less than ideal as a circularly polarized antenna for use in FCC applications.
Therefore, there has been a long-standing need in the community for systems and methods that are FCC compliant and also enable a stub-loop antenna's VSWR to be adjusted without significantly impacting the polarization ratio or vice versus.